This invention relates to an apparatus used in the process of coating a stent, and more particularly provides a suction stent mandrel fixture and method for minimizing coating defects on stents.
Blood vessel occlusions are commonly treated by mechanically enhancing blood flow in the affected vessels, such as by employing a stent. Stents act as scaffolding, functioning to physically bold open and, if desired, to expand the wall of affected vessels. Typically stents are capable of being compressed, so that they can be inserted through small lumens via catheters, and then expanded to a larger diameter once they are at the desired location. Examples in the patent literature disclosing stents include U.S. Pat. No. 4,733,665 issued to Palmaz, U.S. Pat. No. 4,800,882 issued to Gianturco, and U.S. Pat. No. 4,886,062 issued to Wiktor.
FIG. 1 illustrates a conventional stent 10 formed from a plurality of struts 12. The plurality of struts 12 are radially expandable and interconnected by connecting elements 14 that are disposed between adjacent struts 12, leaving lateral openings or gaps 16 between adjacent struts 12. Struts 12 and connecting elements 14 define a tubular stent body having an outer, tissue-contacting surface and an inner surface.
Stents are used not only for mechanical intervention but also as vehicles for providing biological therapy. Biological therapy can be achieved by medicating the stents. Medicated stents provide for the local administration of a therapeutic substance at the diseased site. Local delivery of a therapeutic substance is a preferred method of treatment because the substance is concentrated at a specific site and thus smaller total levels of medication can be administered in comparison to systemic dosages that often produce adverse or even toxic side effects for the patient.
One method of medicating a stent involves the use of a polymeric carrier coated onto the surface of the stent. A composition including a solvent, a polymer dissolved in the solvent, and a therapeutic substance dispersed in the blend is applied to the stent by immersing the stent in the composition or by spraying the composition onto the stent. The solvent is allowed to evaporate, leaving on the stent surfaces a coating of the polymer and the therapeutic substance impregnated in the polymer.
A shortcoming of the above-described method of medicating a stent is the potential for coating defects. While some coating defects can be minimized by adjusting the coating parameters, other defects occur due to the nature of the interface between the stent and the apparatus on which the stent is supported during the coating process. A high degree of surface contact between the stent and the supporting apparatus can provide regions in which the liquid composition can flow, wick, and collect as the composition is applied. As the solvent evaporates, the excess composition hardens to form excess coating at and around the contact points between the stent and the supporting apparatus. Upon the removal of the coated stent from the supporting apparatus, the excess coating may stick to the apparatus, thereby removing some of the coating from the stent and leaving bare areas. Alternatively, the excess coating may stick to the stent, thereby leaving excess coating as clumps or pools on the struts or webbing between the struts.
Accordingly, a new stent mandrel fixture is needed to minimize coating defects.
In accordance with one embodiment, an apparatus for supporting a stent during the process of applying a coating substance to the stent is provided, comprising a mandrel having a hollow tubular body and pores disposed on the surface of the mandrel, the pores extending through the body; and a vacuum device in fluid communication with the mandrel for extracting the coating substance that is applied to the stent. The apparatus can also include a coupling for allowing the mandrel to rotate with respect to the vacuum device. In one embodiment, the apparatus additionally includes a first member connected to one end of the mandrel and a second member connected to the other end of the mandrel, wherein the mandrel is disposed through a longitudinal bore of the stent. The stent can be supported by the first and second members of the apparatus such that the mandrel does not contact an inner surface of the stent. The first member can be moved incrementally closer to the second member for securing the stent between the first and second members.
In accordance with another embodiment, an apparatus is provided, comprising a first member for supporting a first end of a stent; a second member for supporting a second end of the stent; a third member connecting the first member to the second member and extending through a longitudinal bore of the stent, the third member having a longitudinal bore, and the third member having pores on a surface of the third member, the pores extending all the way through the surface to the bore; and a vacuum device in fluid communication with the bore of the third member for applying a vacuum pressure so as to extract any excess coating substance that is applied to the stent during a process of coating the stent. In one embodiment, the first and second members are generally coned shaped and capable of penetrating at least partially into the ends of the stent. As a result, when a stent is positioned on the apparatus, the exterior surface of the third member does not contact the inner surface of the stent during the application of the coating substance. The coned shaped first and second members can be hollow and in fluid communication with the bore of the third member. The coned shaped ends can include pores disposed on the surface thereof for allowing the vacuum device to extract the coating substance that is deposited on the first and second members.
In accordance with another embodiment of the invention, a stent coating device is provided, comprising: a mandrel for being inserted at least partially through a longitudinal bore of a stent, the mandrel having a hollow tubular body and pores formed on the surface of the mandrel, the pores extending all the way through the body; and a vacuum device in fluid communication with the mandrel for collecting excess coating composition that is applied to the stent.
In accordance with another embodiment, a method of coating a stent is provided, comprising: inserting a stent over a mandrel having a hollow tubular body and pores disposed on the surface of the mandrel, the pores extending through the body; applying a coating composition to the stent; and applying a vacuumed pressure to the hollow tubular body for extracting the coating composition that is applied to the stent. The coating composition can be applied by spraying the composition onto the stent. In one embodiment, the stent can be rotated about the longitudinal axis of the stent. The coating composition can include a polymer dissolved in a solvent and a therapeutic substance optionally added thereto. The outer surface of the mandrel can contact the inner surface of the stent. Alternatively, the outer surface of the mandrel does not contact the inner surface of the stent.